Merge branch 'yasu/slack-unfurl-links'

* yasu/slack-unfurl-links:
  show number of changed files in longest shared prefix
  escape and only show first line of commit msg
  update docs with link unfurl
  tests: add unit tests for parsing of GH links
  add route to handle incoming slack event notifications
  parse incoming unfurl links and try to construct supported GH types
  add api route to send slack unfurl request
  add slack atd bindings for url verification and chat unfurl
  add logic for building message body of unfurled commit links
  add slack incoming request signature validation

Author: yasunariw

README.md

@@ -40,6 +40,14 @@ Run the `_build/default/src/monorobot.exe` binary. The following commands are su
         - **Incoming Webhooks:** To use [incoming webhooks](https://api.slack.com/messaging/webhooks), enable them in your app dashboard and create one for each channel you want to notify. Store them in the `slack_hooks` field of your secrets file. If you decide to notify additional channels later, you will need to update the secrets file with the new webhooks and restart the server.
 
 
+### Link Unfurling
+
+You can configure Monorobot to [unfurl GitHub links](https://api.slack.com/reference/messaging/link-unfurling) in Slack messages. Currently, commit links are supported.
+
+1. Give your app `links:read` and `links:write` [permissions](https://api.slack.com/apps).
+1. Configure your app to [support the Events API](https://api.slack.com/events-api#prepare). During the [url verification handshake](https://api.slack.com/events-api#the-events-api__subscribing-to-event-types__events-api-request-urls__request-url-configuration--verification__url-verification-handshake), you should tell Slack to direct event notifications to `<server_domain>/slack/events`. Ensure the server is running before triggering the handshake.
+1. [Register the GitHub domains](https://api.slack.com/reference/messaging/link-unfurling#configuring_domains) you want to support.
+
 ### Documentation
 
 The bot expects two configuration files to be present.

documentation/secret_docs.md

@@ -19,6 +19,7 @@ A secrets file stores sensitive information. Unlike the repository configuration
 | `gh_hook_token` | specify to ensure the bot only receives GitHub notifications from pre-approved repositories | Yes | - |
 | `slack_access_token` | slack bot access token to enable message posting to the workspace | Yes | try to use webhooks defined in `slack_hooks` instead |
 | `slack_hooks` | list of channel names and their corresponding webhook endpoint | Yes | try to use token defined in `slack_access_token` instead |
+| `slack_signing_secret` | specify to verify incoming slack requests | Yes | - |
 
 Note that either `slack_access_token` or `slack_hooks` must be defined.
 

lib/action.ml

@@ -232,4 +232,42 @@ module Action (Github_api : Api.Github) (Slack_api : Api.Slack) = struct
     | Context.Context_error msg ->
       log#error "%s" msg;
       Lwt.return_unit
+
+  let process_link_shared_event (ctx : Context.t) (event : Slack_t.link_shared_event) =
+    let process link =
+      match Github.gh_link_of_string link with
+      | None -> Lwt.return_none
+      | Some gh_link ->
+      match gh_link with
+      | Commit (repo, sha) ->
+        ( match%lwt Github_api.get_api_commit ~ctx ~repo ~sha with
+        | Error _ -> Lwt.return_none
+        | Ok commit -> Lwt.return_some @@ (link, Slack_message.populate_commit repo commit)
+        )
+    in
+    if List.length event.links > 2 then Lwt.return "ignored: more than two links present"
+    else begin
+      let links = List.map event.links ~f:(fun l -> l.url) in
+      let%lwt unfurls = List.map links ~f:process |> Lwt.all |> Lwt.map List.filter_opt |> Lwt.map StringMap.of_list in
+      if Map.is_empty unfurls then Lwt.return "ignored: no links to unfurl"
+      else begin
+        let req : Slack_j.chat_unfurl_req = { channel = event.channel; ts = event.message_ts; unfurls } in
+        match%lwt Slack_api.send_chat_unfurl ~ctx req with
+        | Ok () -> Lwt.return "ok"
+        | Error e ->
+          log#error "%s" e;
+          Lwt.return "ignored: failed to unfurl links"
+      end
+    end
+
+  let process_slack_event (ctx : Context.t) headers body =
+    let secrets = Context.get_secrets_exn ctx in
+    match Slack_j.event_notification_of_string body with
+    | Url_verification payload -> Lwt.return payload.challenge
+    | Event_callback notification ->
+    match Slack.validate_signature ?signing_key:secrets.slack_signing_secret ~headers body with
+    | Error e -> action_error e
+    | Ok () ->
+    match notification.event with
+    | Link_shared event -> process_link_shared_event ctx event
 end

lib/api.ml

@@ -10,4 +10,6 @@ end
 
 module type Slack = sig
   val send_notification : ctx:Context.t -> msg:post_message_req -> (unit, string) Result.t Lwt.t
+
+  val send_chat_unfurl : ctx:Context.t -> chat_unfurl_req -> (unit, string) Result.t Lwt.t
 end

lib/api_local.ml

@@ -20,7 +20,15 @@ module Github : Api.Github = struct
     | Ok file -> Lwt.return @@ Ok (Github_j.api_commit_of_string file)
 end
 
+module Slack_base : Api.Slack = struct
+  let send_notification ~ctx:_ ~msg:_ = Lwt.return @@ Error "undefined for local setup"
+
+  let send_chat_unfurl ~ctx:_ _ = Lwt.return @@ Error "undefined for local setup"
+end
+
 module Slack : Api.Slack = struct
+  include Slack_base
+
   let send_notification ~ctx:_ ~msg =
     let json = msg |> Slack_j.string_of_post_message_req |> Yojson.Basic.from_string |> Yojson.Basic.pretty_to_string in
     Stdio.printf "will notify #%s\n" msg.channel;
@@ -29,6 +37,8 @@ module Slack : Api.Slack = struct
 end
 
 module Slack_simple : Api.Slack = struct
+  include Slack_base
+
   let log = Log.from "slack"
 
   let send_notification ~ctx:_ ~(msg : Slack_t.post_message_req) =
@@ -41,6 +51,8 @@ module Slack_simple : Api.Slack = struct
 end
 
 module Slack_json : Api.Slack = struct
+  include Slack_base
+
   let log = Log.from "slack"
 
   let send_notification ~ctx:_ ~(msg : Slack_t.post_message_req) =

lib/api_remote.ml

@@ -81,4 +81,26 @@ module Slack : Api.Slack = struct
         )
       | Error e -> Lwt.return @@ build_query_error url e
       )
+
+  let send_chat_unfurl ~(ctx : Context.t) req =
+    log#info "unfurling Slack links";
+    let secrets = Context.get_secrets_exn ctx in
+    match secrets.slack_access_token with
+    | None -> Lwt.return @@ fmt_error "failed to retrieve Slack access token"
+    | Some access_token ->
+      let data = Slack_j.string_of_chat_unfurl_req req in
+      log#info "%s" data;
+      let url = "https://slack.com/api/chat.unfurl" in
+      let headers = [ bearer_token_header access_token ] in
+      let body = `Raw ("application/json", data) in
+      ( match%lwt http_request ~body ~headers `POST url with
+      | Ok s ->
+        let res = Slack_j.chat_unfurl_res_of_string s in
+        if res.ok then Lwt.return @@ Ok ()
+        else (
+          let msg = Option.value ~default:"an unknown error occurred" res.error in
+          Lwt.return @@ fmt_error "%s\nfailed to unfurl Slack links" msg
+        )
+      | Error e -> Lwt.return @@ fmt_error "error while querying %s: %s\nfailed to unfurl Slack links" url e
+      )
 end

lib/colors.ml

@@ -0,0 +1,13 @@
+(* https://styleguide.github.com/primer/utilities/colors/#background-colors *)
+
+let gray = "#f6f8fa"
+
+let blue = "#0366d6"
+
+let yellow = "#ffd33d"
+
+let red = "#d73a49"
+
+let green = "#28a745"
+
+let purple = "#6f42c1"

lib/common.ml

@@ -35,3 +35,12 @@ let get_local_file path = try Ok (Std.input_file path) with exn -> fmt_error "%s
 let write_to_local_file ~data path =
   try Ok (Devkit.Files.save_as path (fun oc -> Stdio.Out_channel.fprintf oc "%s" data))
   with exn -> fmt_error "%s" (Exn.to_string exn)
+
+let longest_common_prefix xs =
+  match xs with
+  | [] -> ""
+  | [ x ] -> x
+  | x :: _ -> String.sub x ~pos:0 ~len:(Stre.common_prefix x (List.sort xs ~compare:String.compare |> List.last_exn))
+
+let sign_string_sha256 ~key ~basestring =
+  Cstruct.of_string basestring |> Nocrypto.Hash.SHA256.hmac ~key:(Cstruct.of_string key) |> Hex.of_cstruct |> Hex.show

lib/config.atd

@@ -47,4 +47,6 @@ type secrets = {
   ~slack_hooks <ocaml default="[]"> : webhook list;
   (* Slack bot token obtained via OAuth, enabling message posting to the workspace *)
   ?slack_access_token : string nullable;
+ (* Slack uses this secret to sign requests; provide to verify incoming Slack requests *)
+  ?slack_signing_secret : string nullable;
 }

lib/github.atd

@@ -24,6 +24,9 @@ type commit = {
 type github_user = {
   login: string;
   id: int;
+  url: string;
+  html_url: string;
+  avatar_url: string;
 }
 
 type repository = {
@@ -218,12 +221,19 @@ type file = {
   blob_url <ocaml name="url"> : string;
 }
 
+type api_commit_stats = {
+  total: int;
+  additions: int;
+  deletions: int;
+}
+
 type api_commit = {
   sha: commit_hash;
   commit: inner_commit;
   html_url <ocaml name="url"> : string;
   author: github_user;
   files: file list;
+  stats: api_commit_stats;
 }
 
 type commit_comment_notification = {